2nd-generation mobile communication refers to transmission and reception voice as digital signals, which includes CDMA, GSM, and the like. Advancing from GSM, GPRS has been proposed, which is a technique of providing a packet switched data service on the basis of the GSM system.
3rd-generation mobile communication refers to transmission and reception an image and data, as well as voice. 3GPP (Third Generation Partnership Project) has developed a mobile communication system (IMT-2000) technique and adopts WCDMA as a radio access technology (RAT). A combination of the IMT-2000 technique and the RAT, e.g., WCDMA, is called a universal mobile telecommunication system (UMTS) in Europe. UTRAN is the antonym for the UMTS Terrestrial Radio Access Network.
Meanwhile, with the 3rd-generation mobile communication, data traffic is anticipated to be sharply increased in the future, so standardization has been conducted to make a long-term evolution network (LTE) have a broader bandwidth.
In the LTE, an E-UMTS (Evolved-UMTS) and an E-UTRAN (Evolved-UTRAN) are used, and in the E-UTRAN, OFDMA (Orthogonal Frequency Division Multiple Access) is used as a radio access technology (RAT).
FIG. 1 is a view showing a network architecture of the E-UMTS (Evolved Universal Mobile Telecommunications System), a mobile communication system to which the related art and the present invention are applied.
As can be seen from FIG. 1, the E-UMTS system has been evolved from an existing UMTS system, for which the 3GPP is proceeding with the preparation of the basic specifications applicable thereto. The E-UMTS system may be classified as an LTE (Long Term Evolution) system.
The E-UMTS network can be divided into an E-UTRAN and a core network (CN). The E-UTRAN includes a terminal (referred to as ‘UE (User Equipment) 10, hereinafter), base stations (referred to as eNode Bs, hereinafter) 21, 22, and 23, (referred to as ‘20’, hereinafter), a serving gateway (S-GW) 32 located at an end of a network and connected to an external network, and a mobility management entity (MME) 31 that manages or controls mobility of the UE. One or more cells may exist for a single eNode B 20.
The base station, e.g., the eNode B manages radio resources of one or more cells, and a single cell is set to have one of bandwidths such as 1.25, 2.5, 5, 10, and 20 MHz and provides uplink or downlink transmission service to numerous UEs. In this case, different cells may be set to provide different bandwidths. Cells may be configured to geographically overlap with each other by using a number of frequencies. The base station (or eNode B) 20 provides basic information for accessing a network by using system information (SI) to the UE 10. The SI includes essential information the UE should know to access the base station 20. Thus, the UE 10 is required to receive all the SI before accessing the base station 20, and also, the UE 10 is required to have the latest SI all the time. Also, since the SI is information every UE within a single cell should retain, the base station 20 periodically transmits the SI.
FIG. 2 shows an exemplary structure of a radio interface protocol in a control plane between the UE and the base station, and FIG. 3 shows an exemplary structure of a radio interface protocol in a user plane between the UE and the base station.
The radio interface protocols are based on the 3GPP radio access network standards. The radio interface protocol has horizontal layers comprising a physical layer, a data link layer, and a network layer, and has vertical planes comprising a user plane (U-plane) for transmitting data information and a control plane (C-plane) for transmitting control signals (signaling).
The protocol layers can be categorized as a first layer (L1), a second layer (L2), and a third layer (L3) based on three lower layers of an open system interconnection (OSI) standard model widely known in the communication system.
The layers of the radio protocol control plane of FIG. 2 and those of the radio protocol user plane will be described as follows.
The physical layer, the first layer, provides an information transfer service by using a physical channel. The physical layer and an upper layer called a medium access control (MAC) layer are connected via a transport channel. Data is transferred between the MAC layer and the physical layer via the transport channel. Between different physical layers, namely, between a physical layer of a transmitting side and that of a receiving side, data is transferred, via the physical channel.
The physical channel is composed of a number of subframes present in a time axis and a number of subcarriers present in a frequency axis. Here, a single subframe includes a plurality of symbols and a plurality of subcarriers in the time axis. A single subframe includes a plurality of resource blocks, and a single resource bock includes a plurality of symbols and a plurality of subcarriers. A single resource block is called a slot and has a length of 0.5 ms temporally. A TTI (Transmission Time Interval), a unit time during which data is transmitted, is 1 ms which corresponds to a single subframe.
Physical channels existing in the physical layers of a transmitter and a receiver include an SCH (Synchronization Channel), a PCCPCH (Primary Common Control Physical Channel), an SCCPCH (Secondary Common Control Physical Channel), a DPCH (Dedicated Physical Channel), a PICH (Paging Indicator Channel), a PRACH (Physical Random Access Channel), a PDCCH (Physical Downlink Control Channel), and a PDSCH (Physical Downlink Shared Channel).
The MAC layer, the second layer, is connected with the physical layer through a transport layer, and connected to an upper layer called a radio link control (RLC) layer via a logical channel.
A downlink transport channel for transmitting data from the network to the UE includes a broadcast channel (BCH) for transmitting system information, a paging channel (PCH) for transmitting a paging message, and a downlink shared channel (DL-SCH) for transmitting user traffic or a control message. The downlink multicast, traffic of a broadcast service, or a control message may be transmitted via the downlink SCH or a separate downlink MCH (Multicast Channel). An uplink transport channel for transmitting data from the UE to the network includes a random access channel (RACH) for transmitting an initial control message and an uplink SCH for transmitting other user traffic or a control message.
The logical channel is divided into a control channel that transmits information of the control plane and a traffic channel that transmits information of the user plane according to a type of transmitted information.
The logical channels, which are at an upper position than the transport channel and mapped to the transport channel, include a BCCH (Broadcast Channel), a PCCH (Paging Control Channel), a CCCH (Common Control Channel), an MCCH (Multicast Control Channel), an MTCH (Multicast Traffic Channel), a DCCH (Dedicated Control Channel), and the like.
An RLC (Radio Resource Control) layer, the second layer, supports reliable data transmission, guarantees quality of service (QoS) of each radio bearer (RB), and is responsible for (or handles) data transmission. In order to guarantee RB-specific QoS, the RLC has one or two independent RLC entities for each RB, and in order to support various types of QoS, the RLC layer provides three RLC modes: a TM (Transparent Mode); a UM (Unacknowledged Mode); and an AM (Acknowledged Mode).
A packet data convergence protocol (PDCP) layer, the second layer, performs a function called header compression that reduces the size of a header of an IP packet, which is relatively large and includes unnecessary control information, in order to effectively transmit the IP packet such as an IPv4 or IPv6 in a radio interface having a smaller bandwidth. Also, the PDCP layer is used to cipher data of the C-plane, e.g., an RRC message. The PCP layer also ciphers data of the U-plane.
A radio resource control (RRC) layer located at the uppermost portion of the third layer is defined only in the control plane, and controls a logical channel, a transport channel, and a physical channel in relation to configuration, reconfiguration, and the release or cancellation of radio bearers (RBs). In this case, the RBs refer to a service provided by the second layers of the radio protocol for data transmission between the UE and the E-UTRAN.
When there is an RRC connection between the RRC of the UE and the RRC layer of the wireless network, the UE is in an RRC-connected mode, or otherwise, the UE is in an idle mode.
A non-access stratum (NAS) layer positioned at an upper portion of the RRC layer performs functions such as session management, mobility management, and the like.
The NAS layer illustrated in FIG. 2 will be described in detail.
An eSM (evolved session management) that belongs to the NAS layer performs a function such as a default bearer management, a dedicated bearer management, or the like, and is responsible for (or handles) controlling to allow the UE to use a PS service in a network. Default bearer resource has characteristics in that it is allocated from a network when the UE first accesses a particular packet data network (PDN). In this case, the network allocates an IP address that may be used by the UE to allow the UE to use a data service, and also allocates QoS of a default bearer. In LTE, two types of bearers, i.e., a bearer having guaranteed bit rate (GBR) QoS characteristics that guarantee a particular band width for a data transmission and reception and a non-GBR bearer having best effort QoS characteristics without guaranteeing a bandwidth, are supported. In the case of the default bearer, the non-GBR bearer is allocated. In the case of a dedicated bearer, a bearer having the QoS characteristics of the non-GBR is allocated.
The bearer allocated to the UE by the network is called an evolved packet service (EPS) bearer, and when the network allocates the EPS bearer, the network allocates an ID. This is called an EPS bearer ID. A single EPS bearer has QoS characteristics of a maximum bit rate (MBR) or/and guaranteed bit rate (GBR).
FIG. 4 is an exemplary view showing a relationship between a PDCCH (Physical Downlink Control Channel) and a PDSCH (Physical Downlink Shared Channel), i.e., channels from a base station to a UE.
As can be seen with reference to FIG. 4, in the downward direction from the base station to the UE, the physical channels include the two types of channels, i.e., the PDCCH and the PDSCH.
Via the PDCCH, control information, which is not directly connected with transmission of user data and is required for operating a physical channel, is transmitted. In brief, the PDCCH is used for controlling other physical channels. In particular, the PDCCH is used to transmit information required for receiving the PDSCH. When data is transmitted by using a certain particular frequency band at a certain particular point in time, information regarding which of UEs the data is transmitted for, what size it is, and the like, is transmitted via the PDCCH. Thus, each UE receives the PDCCH at a particular transmit time interval (TTI), and checks whether or not data to be received by each UE is transmitted. When the information indicates that data to be received by each UE is transmitted, each UE receives the PDSCH by using information such as frequency, or the like, indicated by the PDCCH. Namely, information regarding to which UE(s) (one or a plurality of UEs) the data of the PDSCH is to be transmitted, information regarding how the UEs is to receive the data of the PDSCH and decode the same, and the like, may be included in the physical channel PDCCH and transmitted.
Meanwhile, the afore-mentioned mobile communication system provides a service by using a packet switching (PS) technique, and for this PS service, user data is transmitted and received by using an IP among techniques belonging to three network layers in the OSI seven layers.
FIG. 5 is an exemplary view showing an allocation of an Internet protocol (IP) in the system illustrated in FIG. 1.
In FIG. 5, the S-GW (Serving Gateway) 32 and a P-GW (PDN Gateway) 41 serve to provide a data service to the UE, the S-GW 32 serves to transmit and receive user data to and from the UE 10, the P-GW 41 is connected to an external network (e.g., a public Internet) to allow the user to receive a service from a peer entity (e.g., an ftp server). In detail, the P-GW 41 executes an IP allocation function and a DHCPv4 function, and in order to transfer traffic of the UE 10 to the external network, the P-GW 41 serves as a default router allowing the UE 10 to receive an IP service. Also, when the P-GW 41 is within a distance of one hop from the UE 10 connected to the external network, the P-GW 41 serves as an access router.
In order to receive a service in the network, the UE 10 registers its ID (e.g., IMSI) to the network through an attach procedure, to thereby receive a service. During the attach procedure, a default bearer activation is performed through a PDN connectivity procedure, and during this procedure, the UE is allocated an IP address. The default bearer refers to an EPS bearer which is first activated for a new PDN connection, and is maintained in a set state during a life span of the PDN connection.
A connection establishment procedure for a data transmission and reception with the PDN GW by using an IPv4 will be described with reference to FIG. 5.
The UE 10 transmits an Attach Request message to the MME 31. At this time, the Attach Request message may include a PDN Connectivity Request message. Or, the Attach Request may include an APN (Access Point Name). Also, the Attach Request includes information regarding the IPv4, a PDN connection type. When the UE does not include the APN, the network may determine a default APN based on subscriber information of the UE to establish a PDN connection. Or, for the purpose of security, the UE 10 may not include the APN in the Attach Request message and transmit the Attach Request message without the APN after security is activated in a Protocol Configuration Option. z
Then, the MME 31 establishes a PDN connection with the first PDN GW 41. And, the MME 31 designates an IPv4 address for the UE. And then, the MME 31 transmits an Attach Accept message to the UE. The Attach Accept message may include an Activate Default EPS Bearer Context Request message. The Activate Default EPS Bearer Context Request message includes an address of the IPv4.
The UE 10 transmits an Attach Complete message to the MME 31. The Attach Complete message includes an Activate Default EPS Bearer Context Accept message.
And then, the UE sets the address of IPv4. In this manner, a data path is established by using the address of IPv4.
Meanwhile, when the UE wants to transmit and receive by using an address of a different IPv4, the UE 10 transmits a PDN connectivity request to the MM3 31 to thereby establish a connection with a second PDN GW 42, and is allocated an address of the different IPv4. At this time, in order to establish a connection with the second PDN GW 42, an APN different from the APN used in the first connection should be used.